A disk drive, such as a magnetic disk drive, comprises a magnetic disk, spindle motor, magnetic head, and carriage assembly. The magnetic disk is disposed in a case. The spindle motor supports and rotates the magnetic disk. The magnetic head reads data from and writes data to the magnetic disk. The carriage assembly supports the magnetic head for movement relative to the magnetic disk. A head section of the magnetic head comprises a recording head for writing and a read head for reading.
Magnetic heads for perpendicular magnetic recording have recently been proposed in order to increase the recording density and capacity of a magnetic disk drive or reduce its size. In one such magnetic head, a recording head comprises a main pole configured to produce a perpendicular magnetic field, return pole or write shield pole, and coil. The return pole or write shield pole is located on the trailing side of the main pole with a write gap therebetween and configured to close a magnetic path that leads to a magnetic disk. The coil serves to pass magnetic flux through the main pole.
For the purpose of improving recording density, there is suggested a magnetic recording head adopting a high-frequency magnetic field assist recording system wherein a spin-torque oscillator is provided as a high-frequency oscillation element between a main pole and a return pole and a high-frequency magnetic field is applied to the magnetic recording layer from this spin-torque oscillator.
When using as the spin-torque oscillator an oscillator whose element size is as large as a dimension of the main pole in a track width direction, circularly-polarized high-frequency magnetic field intensity (c-Hac) of 410 (Oe) can be generated in a perpendicular magnetic recording layer if oscillation is excellently performed, but the oscillation is not excellently effected in reality, and oscillation of only approximately 180 (Oe) is carried out. It is considered that such a state occurs because a spin wave is excited on an oscillation layer of the spin-torque oscillator and energy is considerably lost. Further, since excitation of the spin wave is suppressed when the element size is reduced, the oscillation is excellent, but produced high-frequency magnetic field intensity is insufficient, and excellent high-frequency assist recording is difficult.